The use of nano-materials with electronic circuit devices to establish field programmable gate array (FPGA) type structures has resulted in different device fabrication methods. One particular method is a cell-based architecture called hybrid nanowire/molecular/semiconductor circuit, which is sometimes referred to as ‘CMOL.’ In this structure, high-density nanowire crossbars and molecular (nanowire junction or bistable junction) switches are fabricated on top of a CMOS stack to build a number of basic logical circuit cells in a logic memory arrangement. This technique is promoted as showing advantages over standard CMOS FPGA structure, such as device density and fault tolerance capabilities.
One key technique used in CMOL is an interface scheme of using special metal pins to provide the electrical connections between nanowires and the CMOS layer. As shown in FIG. 1, a portion 10 of a CMOL structure is depicted in a cross-sectional side view. The CMOS layer 12 supports two special metal pins 14 and 18 above an upper wiring level 13. Each special metal pin 14 and 18 has a different height to connect a CMOS cell electrically to a bottom nanowire 20 or a top nanowire 22. Between the nanowires 20 and 22 are nanodevices 24A, 24B, 24C, and 24D. The nanowires and nanodevices comprise a crossbar 28, generally. Providing metal pins of different heights is difficult to control during the fabrication process. Due to the uniformity of the cell structures, if a pin is misaligned so it connects to a wrong nanowire in one cell, the corresponding mismatch occurs in all other cells. Therefore, appropriate connection of the bottom and top nanowires to the cells in the CMOL structure is crucial.
Another limitation of CMOL structure arises from the high-density characteristics of the nanowires. For example, in the CMOL cell 30 shown in FIG. 2, four CMOS transistors 32, 34, 36, and 38 are provided, however, only the bottom and upper nanowires 40 and 42 may be used to connect to these transistors. More complex circuits requiring additional connections that are independent of the lower and the upper nanowires are not possible in the structure thus described.